Synthetic foundry sands



Patented Mar. 21, 1950 SYNTHETIC FOUNDRY SANDS Burgess P. Wallace. Brooklyn, N. Y., assignor to Whitehead Brothers Company, New York,

N. Y., a corporation of New Jersey No Drawing. Application May 31, 1947, Serial No. 751,637

2 Claims. I

This invention related to the casting in green and dry sand molds of difficulty oxidizable, highmelting-point metals, as grey iron, steel, bronze and the like, but more especially to ferrous metals. Among the principal objects of the invention are the provision of a composite facing sand that possesses decidedly superior facing characteristics whereby the castings obtained when employing such facing sand are remarkably clean, being free from burnt-on sand grains, pits, checks and other defects and, consequently, such castings do not require expensive and tedious cleaning operations as sand-blasting, wire brushing and the like. Other objects of the invention are hereinafter set forth:

In the casting of such high-melting-point metals, it has been a common practice in the foundry industry to face both green and dry sand molds with a layer of specially prepared facing sand, usually composed either of naturally or artificially bonded molding sand and a bituminous coal of high volatile content, such as socalled sea coal for example. In some foundries, coal tar pitch of high melting point has been substituted for some or all of such coal in these special facing sands, it having an especial advantage over sea coal in that it can be used in a high ratio of 90 of sand to one of pitch or even higher ratios for some purposes, whereas the usual sea coal mix is but about 10 to 1.

The special facing sands, whether containing sea coal or pitch as the carbonaceous component thereof, were applied next to the pattern as a facing layer of substantial thickness, usually from to an inch or more in thickness and when the hot molten metal entered the mold cavity the volatile hydrocarbons in the sea coal or pitch in such facing sands were rapidly volatilized by the hot molten metal and the evolved vapors ignited to produce a sooty flame due to the limited supply of unconsumed oxygen present in the mold. As a result of such incomplete combustion, the sand particles at the mold-metal interfac become coated with soot with acts to separate the sand nuclei of such coated particles from the hot metal and thus materially aided in the stripping of the sand layer at such interface from the finished coating.

There are certain disadvantages attendant upon the use of sea coal in facing sand mixtures, among which are the fact that it contains some 60% to 63% of fixed carbon which remains in the sand heap upon the disintegration of the mold and this results in molding difliculties. Again,

sea coal swells on being heated and tends to push 55 the mold apart, especially in the vicinity of the mold-metal interface. Sea coal also contains objectionable amounts, often 3%, of sulphur, which reacts deleteriously with the metal being poured. When heated, it evolves coal gas and coal tar fractions, such as benzene, toluene, tar acids and the like, which fractions not only volatilize without substantial decomposition into soot but do not contain sufficient free carbon to efficiently soot the sand and, consequently, relatively rich mixtures of sand and sea coal, about 10 to 1, must be employed to obtain even a partially effective sooting of the sand particles in and near the mold-metal interface.

Among the disadvantages attendant upon the use of pitch as a substitute for part or all of the sea coal in the aforesaid facing sands, was the tendency of the same to melt at a relatively low temperature, about 300 to 400-F., and upon so melting to freely run around and envelop the naturally bonded sand particles of the mix. Such an action tended to objectionably waterproof either naturally or synthetically bonded sand particles to such an extent that eventually the entire molding sand heap could no longer absorb water or be capable of being properly tempered, so to speak. Coal tar pitch, like sea coal, also has a high fixed carbon content and is equally objectionable in that respect.

My investigations have led to the discovery of a novel composite carboniferous component for a facing sand which can be used in ratios equally as high as the aforesaid pitch-to-sand ratios, which does not swell on heating and hence will not disturb the mold and which contains but a trace of sulphur and no fixed carbon whatsoever -since the carboniferous ingredient completely volatilizes, without melting, at the pouring temperature of the metal. Accordingly, when employing such composite facing sand, there will be no carbon deposits in the sand heaps obtained from the disintegrated molds to cause molding troubles and there also will be no waterproofing of the sand particles during the casting operation, due to the absence in such composite facing sand of any fusible carboniferous component that will melt and flow at the temperatures prevailing in the mold.

The carboniferous component of my improved composite facing sand is preferably prepared as follows:

An aromatic hydrocarbon derivative oi the order of phthalic acid, maleic acid or anhydrides thereof, one hundred per cent volatile at the temperature of the molten metal, is admixed a 3 with a tri-hydrlc or polyhydric alcohol of the so-called glycerol type. such as gbcerine for example, desirably in the proportion of two parts of the derivative selected to one part of glycerine or like alcohol. To this mixture is then added a small amount of a catalyser, desirably about to of either sulphuric or phosphoric acid. The mixture is thereupon heated to a temperature of at least about 338 F. and such heating is continued until foaming of the mixture substantially ceases. Then, Just prior to the final setting of the mixture between about 410 F. and 428 F. the heating is discontinued and the resultant infusible, substantially completely polymerized resinous condensation product, so ob tained, is cooled until it sets into a solid mass. Such condensation product possesses all of the advantages, for use in facing sands for metal casting purposes, of either pitch, sea coal or the like bituminous coals but, being 'infusible, completely volatile and free from sulphur or from fixed carbon, it possesses none of the aforesaid disadvantages of those products. An especial advantage of such resin condensation product is the fact that at the temperature prevailing in the mold cavity, it produces voluminous quantitles of soot which latter functions, as above described, to effectively face the sand with which the condensation product, after the same has been ground, is incorporated and thereby enables the molder to turn out remarkably clean castings, all as above explained. The aforesaid phthalic and maleic acid resins have heretofore 'been of little commercial importance because,-

unlike many of the other synthetic resins used in the molding art, they cannot because of their infusibility be re-melted for molding purposes, once they are formed in a solidified state. However, this very property renders the sam ideally suitable for use in my composite molding sand for the reasons hereinbefore set forth.

While. the aioresaid organic acids and also naphthalene will, when incorporated in a facing sand in very much reduced quantities as compared to the-amount of vsea coal usually employed, function to strip a casting substantially free of sand, nevertheless these acids and their anhydrides volatilize too readily at the temperature prevailing in the mold and release their "volatiles too freely, with the consequence that not only would they be prohibitively expensive for use in foundries, but they would have a deleterious action upon and distort or push apartthe mold.

My improved ground resinous condensation products are adapted to be supplied to metal casting foundries and there incorporated'with the facing sands of the selected grain size, preferably in the proportion of 90 to 1 or 100 to 1, in the same manner as now employed in making special facing sands such as aforesaid with sea coal or pitch. Due their complete volatility ers, linseed oil, rosin, etc. Where a clay-like bond is present in the molding sand, it will have a strong afiinity for water ar d consequently such a molding sand can beii'idily tempered with water and brought up to the proper plasticity or; 511.010.1113 consistency for preparing molds therew Various modifications of and changes in the foregoing compositions and method of making my improved special facing sands may be made without departing from the spirit of the invention as embraced within the scope of the appended claims.

Having thus described my invention, what I claim is: V

, 1. A synthetic mold composition for metal casting purposes, consisting essentially of molding sand having a clay-like bond incorporated therein and also having intimately admixed therewith between about 5% to 5%, by weight of the mold composition, of the solid particles of a ground, substantially completely polymerized, infusible resinous condensation product resulting from the reaction of a polyhydrio alcohol and a member of a group of organic acid compounds consisting of phthalic acid and phthalic acid anhydride and which condensation product is essentially free from fixed carbon and substantially completely volatile at the temperature of molten ferrous metal and when burned in 9. limited quantity of air in a mold during a metalcasting operation is capable of producing voluminous quantities of soot.

2. A synthetic mold composition for metal casting purposes, as claimed in claim 1, wherein the polyhydric alcohol is glycerine.

BURGESS P. WALLACE. REFERENCES CITED The following references are of record in .the file of this patent:

UNITED STATES PATENTS 

1. A SYNTHETIC MOLD COMPOSITION FOR METAL CASTING PURPOSES, CONSISTING ESSENTIALLY OF MOLDING SAND HAVING A CLAY-LIKE BOND INCORPORATED THEREIN AND ALSO HAVING INTIMAGELY ADMIXED THEREWITH BETWEEN ABOUT 1/2% TO 5%, BY WEIGHT OF THE MOLD COMPOSITION, OF THE SOLID PARTICLES OF A GROUND, SUBSTANTIALLY COMPLETELY POLYMERIZED INFUSIBLE RESINOUS CONDENSATION PRODUCT RESULTING FROM THE REACTION OF A POLYHYDRIC ALCOHOL AND A MEMBER OF A GROUP OF ORGANIC ACID COMPOUNDS CONSISTING OF PHTHALIC ACID AND PHTHALIC ACID ANHYDRIDE AND WHICH CONDENSATION PRODUCT IS ESSENTIALLY FREE FROM FIXED CARBON AND SUBSTANTIALLY COMPLETELY VOLATILE AT THE TEMPERATURE OF MOLTEN FERROUS METAL AND WHEN BURED IN A LIMITED QUANTITY OF AIR IN A MOLD DURING A METALCASTING OPERATION IS CAPABLE OF PRODUCING VOLUMINOUS QUANTITIES OF SOOT. 